In 11%, no cancer was found when doctors analysed breast tissue after it had been removed.

In a third, visible signs of the tumour could no longer be detected, and in 17% patients were deemed suitable for lumpectomies rather than mastectomies.

Most of the women had been told they had tumours which were inoperable, and the goal of the treatment was to shrink tumours enough for surgery.

The combination treatment also appears to mean fewer side-effects than with traditional chemotherapy.

Heat treatment

Heat improves the way the drugs work because it draws the liposomes out of the bloodstream directly to the tumour site.

Blood vessels in tumours are leaky, and heat pulls them apart even more - allowing the liposomes to get right into the tumour.

Heat also increases how well the drug is absorbed into the cancer cell and increases oxygen levels in the tumour which makes chemotherapy more effective.

It also increases the DNA damage that chemotherapy does to cancer cells by preventing the enzymes that normally repair such damage.

The researchers have also developed a type of liposomes which melt quickly, so the drug can be delivered into the tumour within 20 seconds of heating.

They melt at 40°C (104°F), warm enough to give the benefits of heat but cool enough to prevent burning the patient's skin.

It is the temperature to which a Jacuzzi is typically heated; hence the treatment's nickname.

Dr Ellen Jones, a radiation oncologist at Duke, said: "By delivering the drugs to the precise site of the tumour, and releasing them at a precise point in time, we'll be able to best utilize their tumour-fighting abilities where they are needed most."

A spokeswoman for Cancer Research UK said: "Treatments that precisely target cancer cells and spare normal tissue will be the cancer therapies of the future."

She added: "Finding effective ways of targeting drugs to the sites of tumours is the focus of much research and there are a variety of methods being tested in the clinic.

"The results from Dr Blackwell's trial are very encouraging and we hope further studies will confirm the effectiveness of the treatment."

The research was presented to the American Society of Clinical Oncology meeting in Orlando, Florida.